Studies of coaxial two-wheeled vehicles comprising wheels at the same wheel axle (shaft) have been conventionally developed because these coaxial two-wheeled vehicles are advantageous from viewpoint of realization of compact configuration in plane shape even as compared to not only four-wheeled vehicle or three-wheeled vehicle, but also different axial two-wheeled vehicle in which rotation shafts (axles) of individual wheels are different like bicycle. However, as long as the problem of stable control of attitude cannot be overcome even in such coaxial two-wheeled vehicle, putting into practice thereof is impossible.
From reasons as described above, as a technique of performing stable control of attitude, e.g., in the Japanese Patent Application Laid Open No. 1988-305082 publication, there is proposed a technology to perform, at short time interval, sampling of inclination (tilt) angles of vehicle body detected by rotary encoder, etc. to calculate control torques of motors for driving wheels on the basis of sampled values, and to instruct the wheel drive motors to perform operations corresponding to the control torques to thereby immediately move, when the vehicle body is inclined, wheels in inclination direction thereof to perform restoration of the vehicle body.
Moreover, in the U.S. Pat. No. 5,871,091 specification, there is proposed a technology to detect inclination (tilt) angle of a vehicle body by plural gyro sensors to perform feedback of the state of the control unit of the motors so that these gyro sensor signals are caused to be horizontal to thereby travel in the state where the vehicle body is maintained to be horizontal.
However, in such coaxial two-wheeled vehicles described in the Japanese Patent Application Laid Open No. 1988-305082 publication and the U.S. Pat. No. 5,871,091 specification, in the case where the human being is ridden, or in the case where the human beings having large weight difference are alternatively ridden, inertia moment and/or load weight when viewed from the motor are changed to much degree so that the control system for stabilizing the attribute becomes unstable. For this reason, there were problems that extraordinary vibration may take place when the human being rides or alights, and/or the operation may be changed by difference between weights of human beings.
Further, there is the problem that the vehicle body may be advanced or reversed by slight movement of center of gravity that a person who rides on the vehicle (hereinafter simply referred to as rider) does not intend. In addition, when position of center of gravity is moved greatly toward forward or backward direction, there was the possibility that the vehicle velocity is excessively increased so that it may fall down.